Bulge-forming apparatus

ABSTRACT

Power cylinders at each end of a tubular workpiece having a force transmitting medium therein operable by the cylinders to force the workpiece into mold cavities. The force transmitting medium is an incompressible plastic such as a polyurethane plug with a memory which returns to its original configuration when the pressure is removed. The retention force between the opposing cylinders is transmitted through the mold die.

United States Patent Kent et al. [4 1 June 20, 1972 s41 DULCE-FORMINGAPPARATUS OTHER PUBLICATIONS [72] In e Ronald KQIIQ f Alvin Tips toSuccessful Bulging With Urethane Rod" by Joseph Rothell rl R ling 8, hof C Turner; pp. 14- 16 of The Tool 8 Manufacturing Engn; Sept. [73]Assignee: McDonnell Douglas Corporation 1968; 61

[ Filed: on. 1970 Primary Examiner-Richard J. Herbst [21] APP] NOJ85,103 Attorney-Walter J. Jason, Donald L. Royer and Robert O.

- Richardson [52] LS. Cl ..72/58, 29/157 T 57 ABSTRACT [51] Int. (I 21d9/05 l [58] Field of Search ..72/54, 58, 60, 61, 62; Power cylinders ateach end of a tubular workpiece having a 29/157 T force transmittingmedium therein operable by the cylinders to force the workpiece intomold cavities. The force trans- Refmnm Cited mitting medium is anincompressible plastic such as a polyu- UNITED STATES PATENTS rethaneplug With a memory which returns to its ong nal configuration when thepressure 1s removed. The retention force 2,603,175 7/1952 Wurzburger..29/ 157 T between h opposing li d i t a mitted through the 2,975,5103/1961 Heuss et a]. ....29/157 T mold i 2,713,314 7/1955 Leuthesser, Jr.et al.. ..72/58 3,220,098 1 1/1965 Arbogast ..29/421 3 China, 7 DrawingFigures a a2 7 n 0 W2 BULGE-FORMING APPARATUS BACKGROUND OF THEINVENTION Ducts other than straight tube or tubing bent on a tube benderare nonnally formed in two or more half shells and welded together tomake a completed duct. Ducts fabricated by this method are high costitems to make and in many cases the quality of the parts results infailures and rejections. Material costs are high due to extra materialrequired for drop-hammer forming.

Bulge formed parts make a stronger, better quality part that willsubstantially reduce the number of rejected parts and total cost. Onesuch apparatus uses a resilient material such as rubber for pushing theworkpiece into the mold cavity. However, at extreme pressures and at theheat thus generated the resilient material deteriorated and its usefullife was too short to be practical. A liquid medium such as hydraulicfluid was tried but at high pressures leakage problems made thisapproach unworkable. In one application oil pressure ruptured theworkpiece before the part could be defonned the desired amount.

When high pressures are used in the deformation of a workpiece, and inparticular when opposing power cylinders are used, great structuralstrength is needed in the interconnection of the parts exerting theforce and the parts having the force exerted thereon.

SUMMARY OF THE PRESENT INVENTION A pair of opposing power cylinders withan interconnecting polyurethane plug within the workpiece is used toexert an outward force on the plug and deform the workpiece outwardlyinto the cavities of the die into which the workpiece had beenpositioned. The power cylinders are interconnected through tensionplates and the die itself. In one forming setup heavy tension platesserve as a base to which the lower die half and the actuating mechanismsare attached. The base plates are positioned on the bed of a press, andthe upper die half interconnects the tension plates attached to the ramof the press. The actuating mechanisms may be spaced apart in accordancewith the length of the dies used. The press provides the necessaryclamping pressure during the forming operafions. The innerlocking designof the forming structure permits all thrust loads to be confined withinthe setup, protecting the press from damage that can occur from theextremely high pressures which can be exerted.

The polyurethane plug has a memory and, after a pressure of 20,000 psi,will return to its original shape in less than seconds. However, it musthave a shore hardness of 90-95 on the D scale of a shore hardnessmachine such as that widely accepted in industry and marketed by ShoreInstruments and Manufacturing Company, Jamaica, New York. The plug alsomust be free from air bubbles to prevent explosion. The plug can be castby pouring it in liquid form into tubing of standard production sizes.lt shrinks slightly as it cures, and fits production tubing perfectlyfor the forming operations. After about 1,000 deformations the plugfinally becomes permanently defonned but can be easily machined back tothe proper diameter and reused indefinitely.

The bulge-forming procedure eliminates the pressure sizing and secondarymetal deposits which were problems in drophammer forming. Specialtrimming, weld smoothing, and other time-consuming hand operations areno longer required. Material thinning, which was a serious problem withdrophammer forming, is inconsequential with this process.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a ductmade by prior art methods;

FIG. 2 is a perspective view, partly broken away, showing theincompressible plastic plug within a tube to be formed;

FIG. 3 is a perspective view of a tube after the first stagebulge-forming operation;

FIG. 4 is a perspective view of the formed tube after final bulge andthe tube is ready for use;

FIG. 5 is a perspective view of another tube shape alter thebulge-forming operation;

FIG. 6 is an elevational view partly in section of the bulgeforrningapparatus in its pre-compression position; and

FIG. 7 is a similar view with the apparatus in compressed position.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS Reference is now madeto FIG. 1 wherein is shown a prior art tubular duct consisting of twohalves l0 and 12 which have been formed by a drip-hammer technique. Thedrop-hammer forming operation stamps the metal into a female die to forma semi-cylindrical section with a T opening portion 14 extendingoutwardly from the'axis of the cylinder. The two sections are thenwelded along their mating edges 16 and 18. After the half sections havebeen welded, tool coordination, trimming and other handling operationsare required which affect the quality and cost.

A similar T shaped duct may be formed in accordance with the presentinvention in which illustrative steps are shown in FIGS. 2, 3 and 4. InFIG. 2 there is shown an annealed tubular blank 20 which may be of someforrnable material such as titanium, stainless steel, aluminum or highstrength material known as lnconel. Within this tubular blank is anincompressible plastic, such as a polyurethane plug 22. One such plug ismade by'Aerolast Company, Inc., 3235 San Fernando Road, Los Angeles,California 90065, and is now available under the trademark of Aerolast2001A. In the bulge-forming process, the blank 20 and plug 22 in FIG.2.are placed into a female die of appropriate shape. Hydraulic pressureis applied to the ends of the plug, forcing the material into thecavities of the die and makingthe tube wall conform to the desiredshape. Split dies with internal cavities are generally used forbulge-forming to provide the shape into which the wall of the tubularblank is forced. If multiple operations are required, the die is made tothe final configuration and spacers are provided which are removedindividually after each operation until the material is incrementallyforced to the maximum depth required. Simple shapes can be formed in asingle operation at reasonable production rates.

FIG. 3 shows the tubular blank 20 after the bulging operation has beenperformed and a portion 24 of the tube has been expanded into a femaledie. The bulge may be cut or ground out and re-annealed before finalforming. FIG. 4 shows the part after the final trimming and ready foruse.

A wide variety of parts can be produced by the bulge-forming technique.The workpieces need not have a straight axis but may be curved orangular or have compound or multiple bulges. Deformable material insheet form may also be. used. The various cross-sections of theworkpiece may be of any configuration before forming, although obviouslythe plug,

workpiece and die must be of compatible shape for the bulgeformingprocess to be efiective. By way of example,.a titanium ring adapter isshown in FIG. 5 wherein the midsection 26 has been bulged out and has alarger diameter than its ends 28 and 30.

Exemplary apparatus for the bulge-forming operation is shown in FIGS. 6and 7. A pair of tension plates 32, 34 are positioned on the bed 36 of apunch press. The upper surface of the plates has grooves 38, 40, 42 and44 to receive flanges 48, 50, 52 and 54 of a pair of opposed powercylinders 56 and 58. These power cylinders may be hydraulically orpneumatically actuated through conduit lines 57 and 59. These powercylinders have pistons 60 and 62 which, when actuated, move inwardly inthe direction of the arrows 64, 66. The lower half of a female die 68has grooves 70 and 72 thereon which fit over the tongues 74, 76 in thetension plates 32 and 34.

The tension plates 32 and 34 may be spaced any desired length apartdepending upon the length of the female die 68' and a spacer block 78 ispositioned therebetween. This block takes bending moments out of the die68 during the bulgeforming operation.

The tube 80 to be formed, with the incompressible plastic plug 82 withinit, is place in the lower half 68 of the female die and then the tophalf 84 of the female die is placed over it. A pair of top tensionplates 86, 88 are positioned over the upper half of the female die 84and have recesses 90, 92, 94 and 96 for engaging the top portions of theflanges 38, 40, 42 and 44 on the power cylinders 56 and 58. Tensionplates 86 and 88 also have tongues98 and 100 for engaging recesses 102and 104 in the upper half of the die 84. A spacer block 106 positionedbetween plates 86 and 88, and between the upper half 84 of the die andthe head 108 of the punch press, removes the bending moment from thedie. Soft metal caps 110 and 112 are at the ends of the plastic plug 82to prevent flow of the plastic from the plug 82 when under pressure.

A cavity 114 is in the lower portion of the die 68 into which thesurface of the tube 80 will be deformed, as shown in FIG. 7. Here isshown mid-portion 112 of the tube 80 depressed into die cavity 1 14 asthe plastic material 82 within the tube 80 has been deformed underpressure from the pistons 60 and 62. The retention forces holding thecylinders 56, 58 in a fixed spaced relationship, while the pistons 60,62 move inwardly, pass through the tension plates 32, 34, 86, 88 and thedie halves 68, 84. After the deformation, the pistons 60 and 62 arereturned to their pre-compression positions as shown in FIG. 6 and bythe time the mold dies are opened, the plastic plug 82 has returned toits original configuration and can readily be removed from the tube 80.

Having thus described an illustrative embodiment of the presentinvention, it is to be understood that other embodiments will occur tothose skilled in the art and that these modifications are to beconstrued as part of the present invention.

We claim:

1. A bulge-forming apparatus for deforming a workpiece comprising:

a female die having an internal cavity therein, said die being adaptedto receive said workpiece therein,

an incompressible plastic plug within said die,

pressure means exerting a pressure on said plug to force said workpieceinto said cavity,

said pressure means comprising a pair of opposed power cylinders withpistons protruding into said die and engageable with said plug, andretention means for retaining said cylinders in predetemtined spacedrelationship,

said retention means including tension plates interconnecting said powercylinders to said die said tension plates having grooves and said powercylinders having flanges thereon adapted to fit within said grooves toprevent lateral movement therebetween, said die and said plates havingcoordinating tongues and grooves to prevent lateral movementtherebetween, and

means for applying forces normal to said tension plates to retaininterlocking of said plates, cylinders and die when pressure is appliedto said plug.

2. A bulge-forming apparatus as in' claim 1, and spacer blocks betweensaid tension plates to permit varied spacing of said cylinders toaccommodate dies of various lengths and to remove bending moments fromsaid dies.

3. A bulge-forming apparatus as in claim 1 wherein said plug is of apolyurethane plastic material deformable under pressure and has a memoryto return to its original configuration when said pressure is released,and

wherein said plug is air bubble free polyurethane having a shorehardness of from to on the D scale.

1. A bulge-forming apparatus for deforming a workpiece comprising: afemale die having an internal cavity therein, said die being adapted toreceive said workpiece therein, an incompressible plastic plug withinsaid die, pressure means exerting a pressure on said plug to force saidworkpiece into said cavity, said pressure means comprising a pair ofopposed power cylinders with pistons protruding into said die andengageable with said plug, and retention means for retaining saidcylinders in predetermined spaced relationship, said retention meansincluding tension plates interconnecting said power cylinders to saiddie said tension plates having grooves and said power cylinders havingflanges thereon adapted to fit within said grooves to prevent lateralmovement therebetween, said die and said plates having coordinaTingtongues and grooves to prevent lateral movement therebetween, and meansfor applying forces normal to said tension plates to retain interlockingof said plates, cylinders and die when pressure is applied to said plug.2. A bulge-forming apparatus as in claim 1, and spacer blocks betweensaid tension plates to permit varied spacing of said cylinders toaccommodate dies of various lengths and to remove bending moments fromsaid dies.
 3. A bulge-forming apparatus as in claim 1 wherein said plugis of a polyurethane plastic material deformable under pressure and hasa memory to return to its original configuration when said pressure isreleased, and wherein said plug is air bubble free polyurethane having ashore hardness of from 90 to 95 on the D scale.